With the ready availability of video tape recordings and domestic equipment upon which they can be played, there is a need to restric access of certain groups of people to certain classes of program. For example it might be desired to prevent children viewing certain classes of material, for example pornographic or violent movies. Traditionally, such security needs have been addressed by physically preventing unauthorized persons from having access to restricted recordings. This method is becoming less practical as the availability of both videotapes and machines to play them increases. For example, parents who wish to have pornographic videotapes in the home, for adult viewing only, risks a child finding the tape and playing it in the parent' absence.
It is therefore desirable to provide means whereby display of preselected classifications of program material can be viewed only by authorized persons.
Arrangements for making video pragrams available to only authorised viewers have long been used in the context of subscription television services and the like. These schemes commonly use a form of scrambling to make the signal unintelligible except to authorized persons in possesion of appropriate un-scrambling means. While it would be possible to apply similar techniques to video programs, for example scrambling pornographic movies, this would have the undesired consequence of rendering these tapes unusable to all persons who do not have special replay means. For many purposes, such as the domestic situation cited above, it is desirable that in the default condition, that is when using standard equipment, the tape plays normally. This means that a specially equipped tape player is only required if it is desired to take advantage of the restricted viewing capability.
Prior-art video security means have also been directed to providing control of viewer access by the party from whom the program originates. This is not always satisfactory, for example in the case of parental control of children's viewing, it is desirable that the parent, rather than the publisher or supplier of the video tape, be able to select whether a given tape will be viewable or not.